1. Field of the Invention
The present invention relates to a developing unit and a developer stirring and transporting method.
2. Description of the Related Art
Heretofore, as something to discharge a developer in a developing unit from the developing unit, there is one to discharge a developer by overflow from a developer discharge port formed in a side wall of the developer. In this structure as stated above, there is known a technique in which in order to cause the overflow more easily, in a second stirring and transporting member to stir and transport a developer, a rotary wing in the vicinity of the developer discharge port is changed to a rotary wing with a transporting force lower than normal, so that the developer top surface height in the vicinity of the developer discharge port becomes locally higher than that in another area (see, for example, JP-A-2000-81787).
However, since the fluidity of the developer is changed according to the use environment, according to what is disclosed in the related art, for example, when used in a high humidity environment such as a temperature of 30° C. and a humidity of 80%, the developer contains water, the fluidity becomes poor, and it becomes hard to discharge. Thus, there arises a disadvantage that the developer is accumulated more than necessary, and it is not discharged unless the volume is much increased. Besides, since the amount of surplus developer discharged becomes smaller than the amount of developer supplied into the developing unit, the amount of developer contained in the developing unit is significantly increased, and the developer can leak from the developing unit. Thus, it becomes necessary to enlarge the developing unit more than necessary in expectation of the amount of developer increased in the developing unit. Besides, with the increase of the developer, the stirring performance is lowered, and therefore, an insufficiency of density is caused, and it becomes difficult to keep high picture quality.